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OBJECTIVE: Centrally released arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) have been shown to participate in brain volume regulation. The aim of the present study was to evaluate the effects of centrally administered AVP and ANP on the time course of development of brain edema in vivo in hyponatremic rats, using diffusion-weighted magnetic resonance imaging.

METHODS: We performed intracerebroventricular (ICV) administration of 120 μg AVP, 20 μg ANP, or physiological saline into the right lateral ventricle in 18 rats. Twenty-five minutes after the treatment, we induced systemic hyponatremia by the intraperitoneal administration of 140 mmol/L dextrose solution. Serial diffusion-weighted imaging scans were obtained up to 96 minutes after the start of the hyponatremia. Changes in the brain extra-to intracellular volume fraction ratio were estimated as changes in the apparent diffusion …